Definition
A ground-based radio navigation transmitter that provides horizontal (left/right) guidance to the runway centerline during an instrument approach. It is the lateral component of an Instrument Landing System (ILS) and transmits on a VHF frequency between 108.10 and 111.95 MHz. The aircraft's navigation receiver interprets the signal and displays a course deviation indication, allowing the pilot to fly the extended runway centerline down to landing.
Plain English
A radio beam from the airport that tells the pilot if the aircraft is lined up with the runway, or off to the left or right. It only handles side-to-side guidance, not up and down.
Context Anchor
Seen on instrument approach charts, cockpit navigation displays, and radio navigation setup for approaches that use a localizer signal.
Derivation
From 'localize' — to fix the position of something. The localizer 'localizes' the aircraft onto the runway centerline. LLZ is the standard ICAO shorthand used internationally on charts and in NOTAMs.
Why Pilots Care
Precise localizer alignment is essential for conducting safe landings when visibility is too low for visual references.
Intuition Check
Do not think of a localizer as a general locator that tells you where the airplane is. It gives one specific kind of guidance: left or right of the runway approach path.
Example Sentence 1
Cleared for the ILS approach, the pilot intercepted the localizer and tracked it inbound to the runway.
Example Sentence 2
A slight left deviation on the localizer called for an immediate heading correction to stay on course.